Digital data storage devices are utilized for storing information for use by data processing systems including computer systems. One commonly used data storage medium is tape storage, used in tape libraries, well suited for backup operations as well as for providing archival and retrieval operations for vast quantities of information content. In this regard, optical storage is also known for voluminous content storage and retrieval.
Tape libraries are known in the art. An example tape library comprises a semi-cylindrical array of tape cartridge storage slots aligned generally along a fixed radius of curvature. A central cartridge inventory is maintained by a library controller, so that logical requests for a particular drive and cartridge may be translated by the library controller into physical device locations and electromechanical operations. In this prior example, a media loader includes a robotic arm rotating at a focus of the cylindrical segment that is elevated and rotated to a particular cartridge storage slot. A picker-gripper mechanism of the arm then “picks” and “grips” the cartridge stored in the slot and moves the cartridge out of the slot and into a temporary transport slot of the arm. The robotic arm is then commanded to perform a second rotation/elevation operation in order to present the retrieved tape cartridge to a loading tray of the selected tape drive, and the tape drive then loads the cartridge and threads the tape for recording/playback operations, following initial setup and calibration routines conventional with tape drives. The drive may be one of several drives accessible by the robotic arm.
Each tape in the library can be recorded on, and read from, by different tape drives in that library and in other libraries. Interchangeability of tapes written by different tape drive (magnetic recording devices) is difficult because different tape drive heads have different record/playback performance on the same tape, causing different error rates. During a write process, data blocks are written and then read back to check for errors (e.g., CRC check). Bad blocks (e.g., blocks that fail the CRC check) are re-written, wherein a good reader/writer head pair does not re-write many blocks but a weak reader/writer pair re-writes many blocks. These blocks are usually re-written on a different reader/writer pair in a different location on tape to overcome said read errors. As such, if a tape drive includes good reader/writer heads, writing on a tape with the good reader/writer pair does not require rewriting many blocks because the reader/writer can transfer data to/from the tape with high quality. However, when data blocks are successfully written on a tape in a first tape drive, and then during a read process an attempt is made to read those blocks from the tape using a second tape drive with a weak reader, the second tape drive may generate a hard read error. A hard read error is generated if too many bad blocks (i.e., errors) are found during the read process, and the tape drive cannot correct those errors. Once a hard read error is generated, the tape drive cannot continue reading data and customer data may not be recovered.
Multiple manufacturers of the tape drive heads further complicate the ability to insure media (e.g., tape) interchange in removable media devices (e.g., tape drive) with essentially the same error performance. Prior approaches, attempt to solve this problem by tightening the specifications of the magnetic recording devices, or heads, such that all devices perform the same or as close as possible in record/playback operation. By tightening the tolerances so that all heads are built essentially exactly the same, each head provides similar error performance as others. However, because it is unlikely for one manufacturer to make all the heads exactly the same, it is even more unlikely that multiple manufactures can produce heads that are within this tightened specification.
There is, therefore, an unsolved need for improving error performance in removable and interchangeble media devices.